1. Field of the Invention
The present invention relates to a device and a method for correcting the injection behavior of at least one injector, by ascertaining information about the at least one injector by comparing setpoint values with actual values individually at a plurality of test points of the at least one injector.
2. Description of Related Art
A device according and a method for correcting the injection behavior of at least one injector, in which the correction information is correction quantities for a quantity correction map of the injector, are described in published German patent document DE 102 15 610. In the case of this device, which is also known as IMA (individual quantity comparison device), and the method, the activation time is corrected in relation to a nominal characteristic map 210 (see FIG. 2) in a control unit individually for each injector, as a function of the setpoint quantity and rail pressure, thereby approximating a desired setpoint quantity as closely as possible. For example, four test values from manufacturing, for example the injection quantity at four different test points, are stored in the control unit during installation for each injector. A correction quantity map 220 (see FIG. 2) is established from these variables, using interpolation methods, as a function of the setpoint quantity and fuel pressure. This characteristic map is essentially a quantity error map. At a given rail pressure, a corrected quantity requirement is then calculated in the control unit for a setpoint injection quantity, using the quantity error map. On this basis, inverted nominal characteristic map 210 of the injector is then used to determine an activation time. An example of this type of quantity correction at one of the test points is described on the basis of FIG. 3, error-free measurements being assumed. During the injector test, a quantity qp, actual, which deviates by Δq from nominal quantity qp, setpoint, is measured for activation time tp. During injector operation, therefore, a quantity requirement qp,setpoint is then reduced by Δq to qmod, which results in an activation time tcorr via the nominal characteristic. If the real and nominal characteristics are parallel, quantity Qp,setpoint is injected by the injector activated for an activation time tcorr. However, if the two characteristics are not parallel, the resulting injection quantity qcorr is not equal to the quantity requirement, even though the injector was tested at the appropriate point.
Devices and methods of this type are used, in particular, for electrically operated injectors for injecting diesel fuel, for example in common rail systems. In the case of common rail injection, pressure generation is decoupled from the injection process. The injection pressure is generated independently of the engine speed and injection quantity, and is provided in the rail for injection. The injection time and quantity are calculated in the electronic engine control unit and transferred from an injector to each engine cylinder via a remote-controlled valve.
A problem with the method described above is the fact that the quantity requirement is first corrected, and the injector characteristic is applied only afterwards. This means that the slope of the injector characteristic must remain constant in the area of the monitored operating point and correspond to the slope of the nominal characteristic. However, these are highly simplified assumptions, which in large parts of the working area do not apply and thus impair the accuracy of the method.